A fuel supply system for a vehicle is known in the art, according to which the fuel supply system has a low-pressure pump and a high-pressure pump. In such a fuel supply system, fuel stored in a fuel tank is pressurized by the low-pressure pump to a relatively low pressure and then low-pressure fuel is further pressurized by the high-pressure pump to a relatively high pressure. In addition, high-pressure fuel is injected into a cylinder of an engine by a high-pressure injection valve, while the low-pressure fuel is also injected into the cylinder by a low-pressure injection valve. In this fuel supply system, a branch-off portion is provided in a connecting pipe, which connects the low-pressure pump to the high-pressure pump, in order to supply the low-pressure fuel flowing in the connecting pipe to the low-pressure injection valve.
In the fuel supply system of this kind, the fuel flowing through the connecting pipe is sucked into an inside of the high-pressure pump, in order that the fuel is pressurized by the high-pressure pump to the relatively high pressure. As a result, fuel pressure in the connecting pipe temporarily becomes lower than the fuel pressure pumped out by the low-pressure pump. On the other hand, a part of the fuel sucked into the high-pressure pump is pushed back into the connecting pipe, when the high-pressure pump controls fuel pressure and/or fuel amount to be pumped out therefrom. Accordingly, the fuel pressure is largely changed in the connecting pipe. Vibration may be generated in the connecting pipe by the change of the fuel pressure.
A fuel supply system, for example, as disclosed in Japanese Patent Publication No. 2006-504903 (=WO 2004/040127), has a valve device, which allows a fuel flow in a forward direction from a low-pressure pump to a low-pressure accumulator and which further allows a fuel flow in a reverse direction from the low-pressure accumulator back into a connecting pipe provided between the low-pressure pump and a high-pressure pump when fuel pressure inside of the low-pressure accumulator becomes higher than a predetermined value.
In the valve device of the fuel supply system according to the above Patent Publication, a first valve member is provided for allowing the fuel flow in the forward direction and a second valve member is provided for allowing the fuel flow in the reverse direction. In addition, a first spring is provided in order to bias the first valve member in a direction to the connecting pipe and a second spring is provided in order to bias the second valve member in a direction to the low-pressure accumulator. The second spring is arranged in the valve device on a side to the connecting pipe provided between the low-pressure pump and the high-pressure pump.
According to the above valve device, the first spring and the second spring are coaxially arranged in a valve housing on a center axis of the valve device, so that the first spring and the second spring are partly overlapped with each other in a radial direction of the valve housing. As a result, a size of the valve housing in the radial direction is large. In addition, a second valve seat, with which the second valve member is operatively brought into contact, is formed in the first valve member. Therefore, a shape of the first valve member is complicated. A manufacturing cost thereof becomes thereby higher.